Catalytic converters intended for control of noxious exhaust emissions from combustion engines are generally of unitary construction, consisting of a catalyst bed sized to hold a specific volume of catalyst and a housing which defines a chamber for directing the exhaust gases through the catalyst bed. The housing includes inlet and outlet extensions which permit the unit to be installed in an exhaust system. The permanency of the aforementioned type of construction wherein the parts are usually assembled by welding precludes any means of disassembly other than to cut through the welded junctures, which, in most cases, is impractical to do. Thus, to inspect, refill, repair or replace the inner components of a converter would not be a practical consideration.
Another restrictive feature of a unitary construction can be seen in the lack of interchangeability of components. For example, the catalyst bed and housing components are generally fabricated to dimensions which provide for a specific catalyst volume. If a different catalyst volume is desired, it is generally necessary to fabricate a different set of components having dimensions which relate to that desired catalyst volume. Although many patents such as U.S. Pat. Nos. 3,186,806; 3,544,264; 3,773,894; 3,775,064; and 3,793,830, for example, show catalytic converters comprising a series of spaced beds, the exhaust gas flow in these arrangements must move serially through all of the catalyst beds with a resulting increase in back pressure. The aforementioned patents dislcose devices in which the capacity is predetermined in that the housings are designed for a certain number of catalyst beds. U.S. Pat. No. 3,687,637 and Canadian Pat. No. 588,160 each show catalytic converters in which a number of catalyst-containing modules may apparently be stacked together. However, like the aforementioned prior art patents, the exhaust gases must flow serially through all of the catalyst chambers and are thus subjected to ever increasing back pressure as the number of modules increases.